EFI and Tuners Dictionary !

Thanks to JeepsandGuns for building and maintaining this EFI and Tuners Terms dictionary! It will be a constant update process as we find new terms or better definitions.

Scroll down for Tuners Terms!

EFI Terms

Lbs/Hr = Pounds Per Hour a term. Most commonly used as a measurement of the flow rate of fuel injectors.

ALDL = Assembly Line Diagnostic Link. This is the plug, usually mounted on the underside of the dash that’s a direct connection to the ECM/PCM and is used to read trouble codes, and datalog. This is what you will connect your laptop to.

CEL = Check Engine Light. A light bulb in dash board. Will light up when the ECM/PCM finds there is a problem and sets a trouble code.

CTS = Coolant Temperature Sensor. A variable resistance sensor that is installed in the engine somewhere it can take a reading of the engine coolant temp. Usually on the intake close to the thermostat. It’s used to let the ECM/PCM know the temp so it knows if the engine is hot or cold. Cold engines require more fuel. Also, ECM/PCM's are set to go into closed loop at a specific temp.

CCP = Charcoal Canister Purge a valve that can be controlled by the ECM/PCM. For emissions it is used to collect hydrocarbons from raw fuel and vent back to gas tank so no hydrocarbons are released into atmosphere.

DIS = Distributor-less Ignition System An ignition system that does not use a distributor. Instead it uses coil packs and ignition timing is triggered from the crankshaft by a trigger wheel.

ECM = Engine Control Module. This is the computer that controls your fuel injection. It controls the engine only.

EGR = Exhaust Gas Recirculation. Allows a small amount of exhaust gas to enter intake to lower combustion chamber temperatures reducing NOX emissions. The EGR valve controlled by a fuel injection computer is controlled by a solenoid to open at programmed times or parameters to allow exhaust gas into the combustion chamber. Works the same as it did on vehicles with a carb, only its controlled by the ECM/PCM instead of coolant temp operated vacuum valves.

EPROM = Erasable Programmable Read-only Memory. This is the chip inside the ECM/PCM that holds the binary file or "tune". This is the part you remove, and read with a chip burner. Normally replaced by an EEPROM when tuning. An EPROM needs a special UV eraser, and is not a good choice for repeated erasing and reprogramming. Not much of the tuning software and hardware still support these chips, however most can still read them.

EEPROM = Electronically Erasable Programmable Read Only Memory. This is the chip most tuners use. It’s erasable by simply putting it into a chip burner and selecting the correct settings for the specific chip with the required software. Can be reused many times.

ESC = Electronic Spark Control. The ESC module is connected to the ECM and a knock sensor. It takes readings from the knock sensor, determines if there is an engine knock or not. If it detects a knock via the knock sensor, it sends a signal to the ECM/PCM to tell it to retard the spark advance until the knock goes away.

KS = Knock Sensor. The knock sensor is used by the ESC to pick up engine knock (or spark knock)

EST = Electronic Spark Timing. Basically it’s the ignition module. It’s connected to the pickup module in the distributor, and to the ECM/PCM to control timing by engine computer.

FPR = Fuel Pressure Regulator regulates the fuel pressure to a set amount. Some are fixed (only one pressure all the time) some are adjustable (can be adjusted by the user) and some are vacuum referenced. A vacuum referenced has low pressure when there is vacuum applied (low/light load, or idle), and higher pressure when there is no vacuum applied (heavy load, wide open throttle).

IAC = Idle Air Control is a stepper motor/valve. The IAC is a "valve" of sorts that is controlled by the ECM/PCM. It has a passage on the throttle body that bypasses the throttle blades and allows air through. By controlling how far open or closed the IAC valve is the ECM/PCM controls the idle speed of the engine.

IAT = Intake Air Temperature. The IAT sensor reads the temperature of the air coming into the intake. It is usually mounted in the air filter housing or air intake tube. It is another measurement used to calculate air density in fuel equation.

MAF = Mass Air Flow. The MAF sensor reads the amount of air coming into an engine. This is an alternative to a MAP sensor, as the ECM/PCM can read the actual amount of air coming into the engine instead of density of air measured in load. Some injection systems use both MAF and MAP sensors. Some use MAP sensor for Barometric reading during key on startup.

MAP = Manifold Absolute Pressure. The MAP sensor reads the amount of vacuum inside the intake manifold. The amount of vacuum is used by the ECM/PCM to calculate the amount of load that is on an engine. A map reading of around 20 KPa would mean low load, a reading of 100 KPa would be high load (wide open throttle) This is used to calculate the amount of fuel that is needed, and also how much spark advance to give.

MAT = Manifold Air Temperature. The MAT sensor reads the temperature of the air inside the intake manifold. As the name states, it’s mounted in the intake manifold instead of the air intake. It is another measurement of air density to calculate with fuel mixture.

MPFI = Multi Port Fuel Injection. A type of fuel injection system where there is a separate fuel injector for each cylinder of the engine. Can also be called PFI, Port Fuel Injection.

NB or NB02 = Narrow Band O2 sensor. Oxygen sensor that’s limited to only a narrow band of readings. Can only detect the normal 14.7 to 1 air fuel ratio. It can only tell if the air fuel ratio is rich or lean. It however can not sense exactly HOW rich or lean the mixture is.

O2 = Oxygen an element. Normally, in the fuel injection world, O2 is used as a short way of saying oxygen sensor. Usually seen as "O2 sensor"

PCM = Powertrain Control Module. This is a fuel injection computer, basically exactly the same as an ECM, however the PCM controls not only the fuel injection, but also controls the shifting of the transmission. Hence the term "powertrain control", controlling both engine and transmission.

SES = Service Engine Soon. Same as CEL = a light bulb. Will light up when the ECM/PCM finds there is a problem and sets a trouble code.

TBI - Throttle Body Injection. A fuel injection system where the fuel injectors are located directly above the throttle blades.

TCC = Torque Converter Clutch. Locks the torque converter so there is no slip, this helps with fuel mileage.

TPS = Throttle Position Sensor. Measures the amount the throttle is opened. Since engine load can change without throttle change, the ECM/PCM needs the TPS to know if the throttle is being opened or closed, and by how much, and how quickly. Things such as Acceleration Enrichment can be based off the TPS readings.

VSS = Vehicle Speed Sensor. Sends pulses (pulse type and number of pulses varies depending on VSS and ECM/PCM) to the engine computer so it knows how fast you are going. The ECM/PCM uses this info to know if you are speeding up, slowing down, or driving steady. On some injection systems this part is not "required" and the system will still function. Just some features will not work. If you’re using a PCM with transmission controls, a VSS is required.

WB or WB02 = WideBand O2 sensor. A wideand 02 sensor differs from a regular or "narrow band" in that is can sense the exact air/fuel ratio. A wideband sensor can not only tell you that your running rich or lean, but can tell you exactly HOW rich or lean you are running. They are very useful for tuning injection systems, and could even be used to tune a carb. However a wideband controller is required to use a WB02, and then also some way to display and record the data from the controller. Its normal output in a 0-5 volt signal. Most common injection systems are not set up to use a WB.

Tuner Terms

AE = Acceleration Enrichment. This is basically like an accelerator pump in a carb. It gives an extra shot of fuel when you hit the gas.

AFR = Air Fuel Ratio. The ratio of how much air and how much fuel are mixed together. The most common you will see is 14.7; this is what’s usually regarded as the desired ratio. The larger the number, the leaner (less fuel) the mixture is, and the smaller the number, the richer (more fuel) the mixture is.

Asynchronous Fuel Mode = This is a temporary mode in which the injectors are commanded on longer for transient conditions. The accelerator pump shot is an asynchronous mode function in which extra milliseconds are added to the injector pulse width when the throttle position sensor rapidly
changes state.

BIN = Binary. Most commonly referred to as the file on chip. Binary is a form of computer code formed of zeros and ones. Its is how the info is stored on the EPROM. Most commonly seen as a bin file. This is what you use your tuning software to view. It displays the bin file in a format you can understand.

BARO = Barometric Pressure. Reading taken at key on before start of atmospheric pressure.

BLM = Block Learn Multiplier. Block Learn Mode term is long term fuel trim. BLM value tracks the Integrator but has a delay. If the Integrator increases so does the BLM, but the BLM lags behind the Integrator. The higher the Integrator climbs above 128, the faster the BLM rises. BLM value affects the VE table by adding fuel above 128 and subtracting fuel below 128

BPC = Base Pulse Constant is a term that is calculated from the volume of one cylinder, the flow rate of one injector,
and a constant that converts the units to match other terms.

BVC = Battery Voltage Correction is a term that corrects the fuel delivery rate for different battery voltages. The injector response is enhanced at higher voltages and is a bit sluggish by comparison at lower voltages. This term is a correction to offset the change in injector response due to battery voltage fluctuations.

INT = The short term fuel trim value is called the Integrator The value of the integrator varies above and below 128 with 128 being no correction. For example, if the Integrator is 135, the ECM is adding fuel because the 02 sensor is reading a lean mixture. If the Integrator is 110, the ECM is removing fuel because the 02 sensor is reading a rich mixture. Anytime the system is not in closed loop, the Integrator will immediately return to a value of 128 and stay there.

BPW = Base Pulse Width. This is basically how quickly the injector are opening and closing. A small (or short) BPW, the injectors are opening and then closing really quickly, letting less fuel through. A larger (or longer) BPW holds the injectors open longer to allow more fuel through.

Closed Loop = This is when the computer is actively taking readings from O2 sensor and uses the data to make constant adjustments and changes to keep the air fuel ratio correct. It adjusts fuel to keep the desired ratio and adjust for things such as changes in elevation and weather.

Open Loop = This is when the computer is running the engine based off preset programming. The computer is not actively making fuel adjustments from O2 sensor. Open loop is usually when the engine is cold. The engine (and 02 sensor) must get to a specific temp before closed loop is allowed. Things such as failed sensors or trouble codes can force open loop.

DE = Deceleration Enleanment. When you let off the gas pedal the ECM/PCM will reduce the amount of fuel going into the engine, as you don’t need as much fuel as you do during normal driving. Keeps you from running rich during deceleration.

DFCO = Deceleration Fuel Cut Off. Reduces the injector BPW to zero, basically shutting off all fuel to the engine during hard deceleration Makes compression braking (using the engine to slow you down instead of the brakes) stronger. Fuel it turned back on if you hit the gas again, or the engine speed drops to a pre programmed rpm.

DRP = Distributor Reference Pulse.

KPa = KiloPascals. A unit of measurement. This is how vacuum is displayed in most all fuel injection tuning. 100 KPa would equal to wide open throttle, no vacuum, 20KPa would equal high vacuums during deceleration.

PE = Power Enrichment. Richens the air fuel ratio during times of hard acceleration for more power. Similar in function to a power valves in a carb.

VE = Volumetric Efficiency is a term that corrects fueling for different engine efficiencies. An engine is basically an air pump and the better the pump; the more power it can generate. Some engines are better pumps than others at a given RPM and MAP condition are, so this term allows the equation to be calibrated for different engines. It is used in open or closed loop. If perfect will produce 14.7 to 1 AFR without other sensor adjustments. It is the most important thing to get that right first because all other adjustments like AE, PE, DFCO and lean cruise are based off that.